Oscillation generator



June 11, 1935. H, MUTH E 2,004,171

OSCILLATION GENERATOR Filed May 2, 1933 INVENTORS HEKBEETMl/Tf/ We 65 7{z BY W ATTORNEY Patented June 11, 1935 J ":2 L

r OYSCILLATION GENERATOR Herbert Muth and Wilhelm Runge, Berlin, Ger

many, assignors to Telefunken Gesellschaft 1 fur Drahtlose Telegraphiem. b. H., Berlin, Germany, a corporation of Germany Application May 2,1933, Serial No. 668,957

' In Germany April 23, 1932 3 Claims. (01. 250-36) i As is well known incircuits for producing oscillations which are return coupled, thefrequency of the oscillations produced is essentially determined by thenatural frequency of theoscilla- 5 tory grid circuit. However, thisfrequency to a small extent is also dependent on the size of all otherimpedances arranged in the circuit. Where a tube is to be operated so asto utilize its total energy and in which the load resistance in the 0anode circuit is adapted to the tube, the produced frequency is to aquite essential degree particularly dependent upon the impedance'of theconsumer. It is dependent, for instance, upon the tuning and coupling ofthe coupled antenna. In order to reduce this undesirable relation it isoften the custom to refrain from directly connecting the consumer to theself excited stage and instead across amplifier stages, in

which case the transmitter is termed a separately controlledtransmitter.

The present invention enables a self excited tube stage to supply largerenergies without the produced frequency being essentially dependent onthe impedance of the consumer.

In accordance with the present invention a return coupling circuit,comprisingreturncoupling means connected in series to the output circuitand utilizing an amplifier tube with high inner resistance in which thecapacitative coupling of the anode with the control electrode iseliminated,

is arranged in such a manner that thezphase, of the potentialstransmitted tothe control circuit by the return coupling is essentiallydetermined only by the phase of the emitting current which leaves thecathode. For attaining the result aimed at by the present inventionscreen grid tubes are suited in particular and also the customary threeelectrode tubes in which, by the use of neutralizing means, inparticular neutralizing capacitative bridges (neutrodyne), thecapacitative coupling of the anode with the control grid across theinner capacity is eliminated.

Figures 1 and 2 are merely given by way of example to illustrateschematically known oscillator arrangements, and Figures 3 to '7 showvarious modifications of the present invention.

If, as was the case hitherto, the tuned grid circuit l of a tube 2 (seeFigure l) is return coupled with the anode circuit, oscillations areproduced whose frequency is determined by the condition that requiresthat the phase of the alternating current voltage applied to the grid Iof thetube 2 through the anode current across the circuit I must beequal to the phase necessary 5 for maintaining the existing anodecurrent. In

inserting into the anode circuit of the tube any impedance 3, therelation between the phases of grid potential and anode current isthereby changed and the frequency of, the produced oscillations hasanother value for which the above relation in phase is again fulfilled;In order to render the influence of the useful impedance arranged in theanode circuit independent of the phase of the current flowing in theanode circuit, and thus also. rendering the frequency of the producedoscillations independent of the changes of the impedance of theconsuming circuit, it is advisable to connect in series with theconsuming circuit 3 a resistance which is high in regard to thiscircuit. This can be accomplished in such manner thattubes are usedwhose inner resistance is high as'compared with the outer impedance.Thus the total impedance of the anode circuit is substantiallyrepresented by the inner resistance of the tube, and fluctuations of theimpedance of the load circuit causeonly slight variations in the phaseof the anode current and of the produced frequency. The use of suchcircuits, namely, in whichfor producing 0scillations a back coupledscreen grid tube is employed, forinstance, and whose inner resistancecorresponds with the above requirements, does however not yet lead tothe desired end. The cause for the produced frequency being muchdependent on the fiuctuationsof the impedance'of the load circuit alsoin such circuits lies in the fact that, in particular for short waves,theleak capacities between the anode and the cathode point present'anessential capacitative parallel connection with regard to the high innerresistance ofthe tube, so that the impedance of the load circuit inregard to the circuit including the return coupling member can no longerbe considered. as being connectedin series to .a high resistance. Theeffective leak capacityis then the capacity between anode and screengrid which in most cases is maintained at cathode high frequencypotential, and, furthermore, the capacity directly between anode and theleads thereof and cathode and the leads thereof. Which of these two leakcapacities predominates by their detrimental action will dependrespectively on the construction of the transmitter. speaking, both acthowever in the same deleterious sense.

In accordance with the present invention the circuit is arranged in sucha manner that the currents passing over the leak capacities, the courseof which is shown in Figure 2 by the dotted capacities 4, do no longerproduce a direct PATENT OFFICE 1 5 Fundamentally of the currents passingthrough the return ecupling member is thus determinedby the high innerresistance of the tube used, and the produced frequency of theoscillations-is.therefore independent of the variations in the impedanceof the consumer.

Figure 3 shows a circuit in accordancewith the present invention inwhich: the detrimental; in-

fluence of the screen grid anode capacity is eliminated. The consumingcircuit in the form of a tuned circuit 3 coupled with an antenna 8 isplaced between anode and screen grid and the return coupling coil 1connected in seriesto the consuming circuit, connects the cathode tothe. screen grid. Thus the currents passing over the anode to screengrid capacity also flow through the return coupling 1. Obviously it isnot. necessary to provide the same return coupling member for thecurrents passing over the screen grid to anode capacity and thoseflowing through the load circuit As indicated in Figure. 4,..it is. alsopossible. to provide a special return coupling coil 1' for. the

capacitative currents. passing,- over. the. tube capacity.

Figure 5 shows a circuit in. which. the leakcapacity formed between the.anode. lead and cathe ode lead is made ineflective. To thisendashield. Bis placed. around the anode. lead, to which however no cathodepotential. is. applied as. is usually the case, but which isconnectedtopoints of the. return coupling coil. 1 carrying. high. ire-Jquency potential. In. the same manner, as. was previously the case. forthe side currents, passing. over the tube capacity, the blind currents.flowing through the electrode lead capacity are utilized for the returncoupling. Also in this case. it would be possible to provide, asin thecase. of Figure 4, a special return coupling member for the parallelcircuit.

Particularly suitableis a combination. of. the two circuits inaccordance with Figure 6', in which. the outer shield is connected tothe screen grid and wherein the blind currents of both circuits arepassed to the return couplingcoil "I.

In the embodiments shown by way. of example the protective shield. andthe. screen grid electrode arev directly connected to the cathode acrossthe return coupling means. It is. obviously within the spirit of theinvention that in providing a connection in the manner described stressmust only be laid in regard to high frequency. Instead of, for instance,providing a conducting connection of the screen grid electrode to thecathode across the return coupling means, and to bridge in this circuitthe screen grid direct voltage source by means of a parallel condenser,as illustrated in the figures, it isalso possible to supply the voltagetothe cathode and screen grid through a direct connection therebetweenblocked against high frequency and to carry the high. frequency from thescreen grid across a blocking condenser to the return coupling member.Such a circuit is shown in Figure '7.

The essential feature of the present invention resides in the fact thatthe phase of the currents of the circuit including the return'couplingmemher is essentially determined by the high tube resistance. It isadvisable therefore in the interest of a greater frequency constancy,although to the detriment of optimum utilization of the energy, not toadapt the consumer to the tube, but to choose a smaller resistancethereof, i. e., to dimension thesarne'in the sense of a subordinateadaptation.

It is-then essential that the choke 9, which, if it were directlyconnected; between anodeand cathode, would again represent, at this timean inductive, bridging for the anode cathode path, is chosen solargethat the parallel connection does not produce. a detrimental efiect orthat the current passing therethrough is likewise utilized for thereturn coupling effect. A

Having thus described our invention and the operation thereof, what weclaim is:

1.. A regenerative oscillation generator circuit comprising an electrondischarge device characterized by high internal resistance having acathode, anode, control grid and screen grid, a tuned input. circuitcoupled between said control grid and cathode, a tuned output circuitconnected be.- tween said anode and screen grid, a coil. indu..- tivelycoupled to said input circuit and having one'terminal connected to thecathode and the: other terminal connected to the screen grid end ofsaid. output circuit whereby the currents in said screen grid and. anodecircuits additively" combine in said coil to affect regeneration.

2;. A regenerative oscillation circuit in accordance withclaim 1,characterized in this that the connection extending from said anode tosaid tuned output circuit is shielded. V

3. A regenerative oscillation circuit in aecordance with claim 1,characterized in this that the connection extending from said anode tosaid.

tuned output circuit is shielded, and a connection is provided betweensaid shieldand said screen grid. 1

HERBERT MUTH. WILHELM RUNGE.

